Teeth

Teeth. A tooth consists of the crown (that is, the portion which projects above the gums), the neck (the somewhat constricted portion of the tooth below the crown enveloped by the gums), and the fang or fangs. On making a section of a tooth, the crown is found to be covered by an outer coating of a very hard substance called enamel; the fang is found to be similarly covered externally by a bony substance, known as the crusta petrosa or cement; the body of the tooth beneath these external covenngs is made up of a substance known as dentine, and this encloses a central1y-situated cavity - the pulp-cavity - which contains the highly sensitive pulp of the tooth, supplied by blood-vessels and nerves, which obtain access to it through an aperture at the extremity of the fang. In the human subject the temporary or milk teeth are 20 in number, each lateral division of each of the jaws containing two incisors, one canine and two molar teeth. The order of appearance of these milk teeth is as follows:- The more centrally-situated incisor appears at about the seventh month, the lateral incisor a month or two later, the anterior molar at the twelfth month, the oanine at the end of about eighteen months, and the posterior molar about the end of the second year. As a rule, the teeth of the lower jaw shortly precede in their appearance the corresponding teeth in the upper jaw. The permanent teeth are 32 in number, each lateral half of each jaw containing two incisors, a canine, two bicuspids or premolars, which replace the temporary molars and three true molars. The first of the permanent teeth to appear is the anterior true molar, which is cut about the sixth year; the central incisor, the lateral incisor, and the two premolars then appear at intervals of about a year each; the canine is cut about the twelfth year, the second true molar a little later, and the third permanent molar or wisdom tooth appears from about the eighteenth to the twenty-fourth year. The permanent teeth are developed in the jaw behind the temporary teeth, which they ultimately displace; and at the age of five years the germs of all the permanent teeth, except the four wisdom teeth, exist ready formed in the jaw of the child, which thus possesses, up to the time when the first milk tooth is shed, no fewer than 48 teeth - viz. 20 milk teeth and the germs of 28 permanent teeth.

Diseases of the Teeth. Dental caries consists in a gradual eating away of the substance of the teeth, which is probably in great part due to the growth of micro-organisms, and which ultimately leads to encroachment on the pulp-cavity. When this occurs, the tooth becomes tender and sensitive to changes of temperatnre and, after a time, exposure of the pulp, with severe toothache supervenes. Inflammatory changes in the pulp itself are then apt to occur, leading to the formation of alveolar abscess. Sometimes the periosteum covering the fangs of the teeth becomes inflamed, and alveolar abscess is set up without previous exposure of the pulp. A common name applied to alveolar abscess is gumboil (q.v.). In the treatment of the diseases of the teeth it is most important to obtain the advice of the dentist from the outset, in order that the mischief may be dealt with before the structure of the tooth is so disorganised as to necessitate its extraction. Temporary relief of the pain, produced by inflammation about the root of a tooth, is often obtained by painting e gum with tincture of iodine; and when a cavity exists and the pulp of the tooth is exposed, a small pledget of cotton-wool upon which one or two drops of creosote have been placed, may be inserted into the cavity, with a view to relieving the toothache until advice can be procured. In view of the suffering entailed by neglect of the teeth, the desirability of the regular and systematic use of the tooth-brush, especially by children, cannot be too strongly insisted upon.